From cbf03f5b38d27573578b13a76b94d3c7470a568e Mon Sep 17 00:00:00 2001
From: chenwuji2000-cyber <chenwuji2000@gmail.com>
Date: Mon, 16 Feb 2026 22:41:05 +0800
Subject: [PATCH] acp_thread: Await Tree-sitter parsing before building agent
 panel diffs (#49101)
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## Summary

Fixes https://github.com/zed-industries/zed/issues/48684

- Await `parsing_idle()` after `set_language()` in both
`Diff::finalized()` and `PendingDiff::finalize()` so that tree-sitter
parsing completes before buffer snapshots are taken for excerpts
- Without this, the 1ms sync parse timeout almost always expires for
non-trivial files, causing excerpts to be created with empty syntax
trees and missing syntax highlighting

## Root Cause

When the agent panel creates or finalizes a diff, it creates a new
`Buffer`, calls `set_language()` (which triggers async tree-sitter
parsing), then immediately proceeds to take buffer snapshots and create
excerpts **without waiting for parsing to complete**. The sync parse
timeout is only 1ms in production (`buffer.rs:1138`), so large files
almost always fail the sync parse and fall back to async parsing — but
no one awaits the async parse before building the diff.

## Fix

Add `buffer.update(cx, |buffer, _| buffer.parsing_idle()).await` after
`set_language()` in both code paths (`Diff::finalized()` and
`PendingDiff::finalize()`). This is the same pattern already used in
`buffer_diff.rs:1728-1731`.

## Test plan

- [x] `cargo test -p acp_thread` — all relevant tests pass
- [x] `./script/clippy` — no warnings
- [x] Manual test: open agent panel, ask it to generate a Python file
with multiline strings (`"""`), verify syntax highlighting is correct
after diff is finalized

Release Notes:

- Fixed missing syntax highlighting for multiline strings in agent panel
diffs
---
 crates/acp_thread/src/diff.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crates/acp_thread/src/diff.rs b/crates/acp_thread/src/diff.rs
index 9e47e70814b01011afc8b854824ae025b524b3f6..8886b458d623237b74f715d3c1d0def33fbefa7d 100644
--- a/crates/acp_thread/src/diff.rs
+++ b/crates/acp_thread/src/diff.rs
@@ -36,6 +36,7 @@ impl Diff {
                     .log_err();
 
                 buffer.update(cx, |buffer, cx| buffer.set_language(language.clone(), cx));
+                buffer.update(cx, |buffer, _| buffer.parsing_idle()).await;
 
                 let diff = build_buffer_diff(
                     old_text.unwrap_or("".into()).into(),
@@ -287,6 +288,7 @@ impl PendingDiff {
         let buffer_diff = cx.spawn({
             let buffer = buffer.clone();
             async move |_this, cx| {
+                buffer.update(cx, |buffer, _| buffer.parsing_idle()).await;
                 build_buffer_diff(base_text, &buffer, language_registry, cx).await
             }
         });